Graphic equalizers are well known in the art. Typically, a graphic equalizer comprises a plurality of filters that each have a variable gain/attenuation associated therewith. The center frequencies for the various filters are distributed across an overall bandwidth having a upper and lower boundary. For example, a typical five band graphic equalizer has five such filters with the following corresponding center frequencies: 100 Hz, 330 Hz, 1 kHz, 3.3 kHz, and 10 kHz.
Graphic equalizers comprise a useful audio processing device, often allowing a listener to compensate for differences in taste or acoustic surroundings as appropriate. Typically, however, prior art graphic equalizers constitute relatively fixed audio processing platforms. Although the gain or attenuation associated with a particular band can be selectively altered by a user, other filter attributes (such as center frequency, filter bandwidth, and step sensitivity) remain fixed. When a particular graphic equalizer has been well matched to a particular audio source, this inflexibility does not typically present a problem. Where, however, a graphic equalizer is intended for use with a variety of different audio sources, problems can arise.
For example, consider a typical prior art five band graphic equalizer for use with a radio that receives both AM broadcasts (in the United States, those broadcasts occurring between 540 kHz and 1700 kHz) and FM band broadcasts (in the United States, those transmissions occurring between 88 MHz and 108 MHz). FM transmissions typically accommodate an audio signal having up to a 15 kHz bandwidth. A typical five band graphic equalizer, though not necessarily optimized for such a signal, will offer reasonable opportunity for useful audio processing. AM broadcasts, however, typically restrict the audio content to a more limited 10 kHz bandwidth. With such a signal, the graphic equalizer high frequency bandpass (or highpass) filter having a center frequency at 10 kHz will obviously support little or no useful audio processing flexibility.
One prior art solution provides a graphic equalizer having a large number of bands. So configured, suitable filters could likely be found to accommodate appropriate processing for most any audio source. While this solution works well in some limited applications, the increased costs and complexity associated with this solution render this approach inappropriate for general application.
Accordingly, a need exists for a graphic equalizer that can better accommodate a variety of different audio sources.